This invention relates to an apparatus for forming a stack of interlocked laminations, e.g. a laminated cylindrical rotor for an electric motor.
Yoshiaki Mitsui U.S. Pat. No. 4,110,895 shows an apparatus for forming and stacking interlockable lamination disks into a cylindrical rotor configuration. The Mitsui apparatus comprises a stationary die structure, and an overhead die structure which is lowered to pierce a strip of material that is indexed along the upper surface of the stationary die structure. The movable die structure includes a circular male die (punch) that is lowered into a chute structure in the stationary die structure to form and sever a circular disk from the strip material during each downstroke of the male die. The circular disks are successively driven downwardly into the chute structure to form a stack.
The chute structure has a female die opening sized to grip the edge of the encircled lamination, whereby successive lamination (disks) tend to remain in face-to-face contact for promotion of interlocking connections between mating projections and holes formed on the opposed disk surfaces. The contact between adjacent laminations is facilitated by a lower support means carried on the piston rod of a vertically-oriented air cylinder. At a predetermined point in the cycle, the air cylinder is operated to compress the stack, thereby achieving (or maintaining) a press fit interlock between the disk projections and mating holes.
A problem with this stacking arrangement arises from the large stacks now required for modern rotors. A large stack results in a heavy, lower end of the stack that is suspended by the interlocking projections on the lowermost disk of the stack gripped in the chute.
During press operations, the impact forces of the punch, and certain rotational forces associated with maintaining parallelism between the laminations, tend to separate the connections between adjacent laminations in the suspended stack. The suspended, lower end of the stack tends to weaken the connections between laminations, as the suspended end increases in height.
The present invention contemplates a different arrangement wherein the lower end of the stack is compressed in a rotatable collet until the stack is dropped from the chute structure. This is advantageous in that the connections between laminations are complete and fully effective. Also, the lamination stack height is maintained without gaps between the laminations.
In carrying out the invention, the collet is adjustable between a first condition wherein its side surfaces grip the edges of the stacked laminations, and a second condition wherein the collet releases the edges of the stack. As the stack is being pushed down through the die, the suspended end of the stack approaches the collet and then is forced through the collet opening. The collet provides vertical support for the stack. When the upper end of the stack has advanced below the die opening, the collet is opened to release the stack, which then drops to a conveyor.
Another feature of the invention addresses the problem of producing a stack of a precise height. The conventional approach is to measure the strip thickness, and then to divide the stack height by the strip thickness to determine the number of disks in the stack. This process is sometimes inaccurate because the strip thickness varies, and the means for measuring the strip thickness is not precise.
The stacking apparatus of the present invention includes a lamination sensing device located a slight distance above the collet for detecting the presence of the lowermost lamination in the downwardly advancing stack. The sensor signal indicates that the stack height corresponds to the distance from the lowermost disk to a reference point at the top portion of the disk opening. The strip thickness is then measured to determine the disks necessary to complete the stack. The overall stack height is more accurate because the partial height of the stack that depends upon measuring the strip thickness is reduced.